At present, *all* the e-mails that I possess - that are from the address in question - appear in Thunderbird wrongly, i.e. the 'display' field in the address book is ignored. So I have no unproblematic e-mails with which to compare the problematic ones (if we require that both terms of the comparison share the same address).
Yet, an opportunity for comparison should arise soon enough, for I'll ask the person concerned to e-mail me from multiple devices.
I am not happy to post a whole 'from' header (which seems large, but I am unsure I am identifying it correctly) here. However, I can look up your e-mail, Jorg, and send it that way instead. I can do that now, or I can wait until I have the header from a fully working e-mail (in which latter case I can send the two headers for comparison).

It should just be a matter to compare the address in the address book with the address in the From: header. You don't need to publish it.
Are you sure you don't have the person in the address book twice? And the other card without the setting?

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